Ruoff. A. L.. J . Chromatoo. 3, 239
(5) Giddings, J. C., J . Chromatog. 2, 44
LITERATURE CITED
E., Zweig, G., “Paper chromatography and Paper Electrophoresis,” second ed., Chap. 3, Academic Press, S e w York, 1958. ( 2 ) Bohemen, J., Purnell, J. H., J . Chem. ( 1 ) 3kwk, R. J., Durrum, E.
SCC.1961, 360.
(3) Giddings, J. C., J . Chem. Educ. 35, 388 (1958). s(4) \ Giddings, J. C., J. Chem. Phys. 31, 1462 (1059).
(1959). (6) Ibid., 3, 443 (1960). ( 7 ) Ibid., 5, 46, 61 (1961). (8) Giddings, J. C., Keller, R. A,, J . Chromatog. 2, 626 (1959). (9) Giddings, J. C., Seager, S. L., J . Chem. Phys. 33, 1579 (1960). (10) Giddings, J. C., Seager, S. L., Stucki, L. R., Stewart, G. H., ANAL. CHEM.32,867 (1960). (11) Giddings, J. C., Stewart, G. H.,
(moj.
(12) Safranski, L. W., Dal Nogare, S., Chem. Eng. News June 26, 102 (1961). RECEIVED for review January 18, 1962. Accepted April 9, 1962. Investigation supported by research grant, A-2402(C4), from the National Institutes of Health, Public Health Service. Division of Physical Chemistry, 140th Meeting, ACS, Chicago, Ill., September 1961.
Direct Application of Gas Chromatography to Atmospheric Pollutants THOMAS BELLAR, JOHN
E. SIGSBY, CLARENCE A.
CLEMONS, and A. P. ALTSHULLER
Robert A. Tuft Sanitary Engineering Center, Division of Air Pollution, Cincinnati 26, Ohio
b The use of a flame ionization detector permits direct determination of hydrocarbons at concentrations found in the atmosphere. Prior concentration of samples in a cold trap i s not necessary. With the system described, the investigators were able to detect the lower molecular weight hydrocarbons found in automotive emissions in controlled irradiation studies. Ease of operation, high sensitivity, and reproducibility are advantages o f the technique. Concentrations as low as 0.001 p.p.m. may be detected in air samples. The experimental parameters required to obtain these results are evaluated. Instrumental modifications required for several applications are discussed, with emphasis upon development of a reliable system with which the hydrocarbons at atmospheric concentrations can be determined routinely.
TI
SE of a gas chromatograph with a
flame ionization detector greatly simplifies the problem of analyzing the wide concentration range of light hydrocarbons found in automotive emissions. This method permits direct analysis of I-cc. volumes of air containing automotive emissions in concentrations of 0.01 to 1.0 p,p.m. Previous methods (1, 3, 4, 8) involved a concentration step to obtain sufficient material to analyze quantitatively. This concentration step was time consuming and gave rise to inaccuracies because of break-through of concentrated compounds with high vapor pressure before enough of the lessabundant compounds could be collected. Flame ionization techniques have been applied to more concentrated samples ( 5 ) ,but in this instance it was desirable to monitor components a t
atmospheric concentrations. The system being monitored was irradiated auto exhaust diluted to concentrations similar to those t h a t might be encountered in the atmosphere ( 7 ) . The irradiated exhaust is contained in a stirred reactor operated in a dynamic fashion, an experimental design which it is hoped will approach atmospheric conditions. Concentration techniques involving large samples proved to be unwieldy and, in our laboratory, a maximum of five samples could be run in one working day. Data on some specific compounds often had to be sacrificed because of differences in col1,ection efficiency and the wide range of concentrations involved. These concentration techniques also depended upon continuous high performance of both equipment and personnel; for example, a small leak in the trap often spoiled a sample. Concentration techniques also allowed the possibility of further reactions in the trap. The method described shows how a small sample of material may be taken out of a continuous stream and analyzed for composition of atmospheric concentrations. A commercially available gas chromatograph with a flame ionization detector is used. EXPERIMENTAL
Equipment. A Perkin-Elmer Model 188 Vapor Fractometer with the third stage modified with PerkinElmer Flame Ionization accessory, and a Minneapolis-Honeywell 0 t o 1 mv. strip chart recorder with a 1-second response were the major equipment used. A Neptune DynaP u m p Model 4K, a wet test meter rated a t 1-liter per revolution, and a Scotchpack bag (heat-sealable plastic) were used for sampling and calibrating
the instrument. Gases used were helium grade A, prepurified hydrogen, and oxygen U.S.P. The hydrocarbons used for calibration were Matheson, CP grade, and Phillips, research grade. The medium activity silica gel used came from Burrell Corp., Pittsburgh, Pa. The Perkin-Elmer Model 188 was rebuilt to a two-stage instrument with the third stage as a completely separate unit (Figure 1). The oven was removed with the cell and syringe sample inlet intact and rotated 180’ so that the thermistor cell was in the correct position for the installation of a flame ionization detector. The pressure regulator and the pressure gage were changed to handle a maximum of 60 p.s.i.g., and the helium flowmeter was replaced with a 0 to 200 cc. per minute flowmeter with suitable calibration data for helium a t the variable pressures used. To help ensure optimum sensitivity and well-defined peaks, the column was attached directly from the outlet of the injection block to the inlet of the flame ioniaation detector rather than through the thermistor block. A by 3 inch type 304 stainless steel tube was silversoldered into a 2-inch section of inch type 304 stainless steel tubing (see expanded drawing), and this tube then was filled with silica gel and attached directly to the main column with a 1/8-inch Swagelok union. Both ends were then packed with Fiberglas to secure the silica gel. The column was attached to the instrument with a l/*-inch rubber compression fitting (synthetic rubber O-ring) and to the flame ionization detector inlet with a 1/16-inch Swagelok nut. The original fixed restrictions on the hydrogen and air supplies for the detector were not used because the flow rate could not be varied to obtain the desired response and reproducibility conditions. I n place of the fixed restrictions, a system of fine metering valves, surge chambers, and flowmeters was used as shown in Figure 1. Oxygen was used in place of air for added sensitivity. With the particular VOL. 34,
NO. 7, JUNE 1962
e
763
2
I
4
CONCENTRATIOh O F ETHYLElrE p p w
Figure 2. METES,hi YILVES
MANOMETER
Figure 1.
Flow schematic
flame ionization detector used, no increase in noise was experienced with oxygen. Column Preparation. The medium activity silica gel was screened for a 40- t o 60-mesh fraction t o remove t h e fines. T h e screened silica gel was heated at 110' C. for 24 hours and then packed, with t h e aid of a mechanical vibrator, into a washed and dried inch 0.d. thin-wall type 304 stainless steel tube, 9 feet long. Operating Conditions. T h e carrier gas flow rate is adjusted to 60 cc. per minute, hydrogen to 42 cc. per minute, and oxygen to 150 cc. per minute. It is necessary t o ignite the hydrogen flame with a n oxygen flow rate of about 400 cc. per minute, because a t 150 cc. per minute a n evplosion occurs t h a t blows the chimney off t h e flame ionization detector. The hydrogen and oxygen flows are not set f o r maximum sensitivity but for maximum convenience because the large volumes of air injected with the sampIe tend to extinguish the flame; however, when the oxygen and hydrogen are adjusted as indicated, the flame
Table 1.
THERHIL CONDUCI Y I T I DETECTOR
reignites spontaneously and reestablishes a constant base line before the ethane peaks. This point is, however, within 5% of maximum sensitivity. It is also suggested that the two bolts holding the chimney to the flame cell be removed The force of any explosion normally will remove the chimney from the cell rather than expanding its energy in a more destructive manner. The column is operated a t room temperature. Sampling System. I n the continuous sampling system, a diaphragm pump was used to move t h e sample continually from the source, a 330-cu. foot dynamic reaction chamber ( 7 ) . A needle valve and water manometer were used to adjust the pressure in the line. With this system it is possible over any interval and under uniform conditions to obtain from the chamber samples of the same volume (see Figure 1). Calibration and Calculations. The calibrations for t h e gaseous hydrocarbons involved Fere obtained by injecting a known volume from a gastight syringe into a Scotchpak bag
Calibration for ethylene
filled with clean air. (The bag showed no memory for the hydrocarbon used in previous runs, if thoroughly flushed.) The air - hydrocarbon mixture r a s thoroughly mixed and then attached to the fractometer sampling system. I n the calibrated volume the negative pressure was adjusted to 1 inch of water, and the exhaust from the pump was routed through a wet test meter to measure the total volume of the gases in the bag. Several samples were analyzed from the bag to ensure that complete mixing had occurred. The manometer then N as disconnected, and the bag was pumped out a t a n increased rate. From the values obtained, the concentration can easily be calculated in parts per million by volume. The plots of peak height us. parts per million (Figure 2 ) have excellent linearity and a standard deviation of 0.3%. Each point shown on
Analyses of Light Hydrocarbons in Irradiation Chamber
Hydrocarbon Concn., P.P.M. Condition C2Ha CtHl CsHS CBHB CdHlo Timea 0.02 8 :49 a.m. Flushed chamber 0.008 0.04 o:Oii 0 YO38 0.11 9:06 a.m. Charging begunb 0.024 0.23 0.013 0.13 0.35 0.068 0 . 8 1 9:26 a.m. 0.02 0.44 0.17 0.086 0.99 10:06 a.m. 0.02 0.19 0.46 0.091 1.03 10:50 a.m. 0.02 0.17 0.47 11:05 a.m. Irradiation begunc 0,053 1.06 0.02 0.19 0.47 11:20 a.m. 0.053 1.06 0.02 0.49 0.16 0.098 1.04 11:50 a.m. 0.02 0.49 0.15 0.099 1.02 12: 20 p.m. 0.02 0.49 0.12 0.101 0 . 9 7 1:25 p.m. 0.02 0.12 0.50 0.103 0 . 9 5 1 : 50 a.m. 0.02 ... 0.087 2 : 50 p.m. 0.059 0.86 ... 0.02 0,075 3 : 20 a.m. 0.099 0.85 0.02 4:20 p.m. ... 0.080 0.101 0.82 Only a Time at which sample was taken, analysis period about 20 minutes. the 30 analyses made during a 7l/z-hour period are given in the Table. b The chamber is a photochemical flow reactor. Banks of warm white and blacklight fluorescent lamps.
~-CIHIO O:O62 0.18 0.22 0 23
0.26 0.25 0.25 0 26 0.27 0.26 0.25 0.25 0.25 14 out of
-
t I
l
~
I
ANALYTICAL CHEMISTRY
l
1
~
l
DILUTE AUTO EXHAUST
Figure 3. A typical chromatogram of automobile exhaust 1. 2.
3, 4,
5, 6. 7. 8.
9.
764
l~
Ethane Ethylene Propane Acetylene lrobutane n-Butane Propylene n-Pentane lsopentane
I
T
’
40
I
1 #4
.4
T
15/oo !!LO
12‘03
TIME
,b:
Figure 5. Chromatogram luted atmosphere
I 2s.
3c-
- .
1. 2. 3.
TYPICAL RESULTS
Figure 4.
Ethane Ethylene Propane
4. 5. 6.
of
a pol-
Acetylene lsobutane n-Butane
Results for ethylene and acetylene
this graph is the average of a t least three determinations. The standard deviation is calculated from the six points at one concentration. Peak height is used since area measurements from the chromatograms were time consuming and proved to be more inaccurate than peak heights due to the small half width involved. For ethane. ethylene, propane, and acetylene, peak heights could be used because the sampling system injected the samples under essentially identical conditions. These calibrations were checked weekly to make slight adjustments for changing column conditions. A calibrated volume of 1.18 cc. (including the internal volume of the injection valve) was used for all runs. The minimum peak measurable is equal to t h a t for about 0.001 p.p.ni. of ethane. Still higher sensitivity can be obtained, if required, by injecting a larger sample volume through the column; honever, this practice decreases the column life, since contaminants are trapped in the column. .ibout 200 1.18-cc. samples of dilute auto exhaust can be injected into the column before the influence of thc trapped contaminants causes the acetylene and the isobutane peaks to combine. By heating the column to 110” C. while back flushing it with He for 24 hours, the analyst can regenerate the column several times RESULTS
A chromatogram taken during a regular automobile exhaust run is shown in Figure 3. There is excellent resolution between peaks representing 0.007 p.p.m. of propane and 1.13 p.p.m. of ethylene. By this method about 30 samples per run may be analyzed; this number is adequate to follow the course of the reactions occurring within the system. Typical results for some components are plotted in Figure 4. The values from 7:30 to 8:30 a.m. are background values of air in the chamber. At 8:30 a.m. the chamber was charged with dilute exhaust; irradiation was begun at 11 a.m. Data for six hydrocarbons from another run are given in Table 1.
The sampling interval is limited by the analysis procedure. A nem sample was taken, after n-pentane passed through the column. The retention time for n-pentane is about 18 minutes, but is somewhat dependent upon the age and history of the column. Apparent deviation between analyses, as shown by the curves in Figure 4, is about 1% in normal operation. Care must be exercised t o maintain the pressure in the 1-cc. volume at the same level. An error of 0.1 inch of water will cause errors as large as 3 to 5%. The utility of the method in atmospheric analysis may be seen in Figure 5. This is a chromatogram taken during a period of moderate pollution, when the oxidant level was approximately 0.1 p.p.m. I n the immediate vicinity of the sampling location there was no traffic, and therefore the values are probably average for the area. Values for two runs are shown in Table 11. At an assumed signal-to-noise ratio of 2 to 1, the limit of detection if peak height data are used ranges from 0.001 p.p.m. for ethylene to approximately 0.04 p.p.m. for n-pentane. If peak areas are used instead of peak heights, the sensitivity for n-pentane would of course be even greater than that for ethylene. The large acetylene-to-ethylene concentration ratios in Table I1 are unusual, when compared with irradiation chamber data and with data
Table
11.
Analyses of Samples
Atmospheric
Hydrocarbon Concentrations, P.P.M. Run 2 Run 1 Ethane Ethylene Propane Acetylene n-Butane
0.007 0.004 0.002 0,020 0.003
0.0066
0.0038 0.001 0.020
0.003
recently collected from a field study in Los Angeles. Several previous investigators have discussed the limits of detection with flame ionization detectors. Ongkiehong (6) calculated a practical detection limit of 0.001 p.p.m. for n-butane. Condon, Scholly, and Averill ( 2 ) obtained a detection limit of 0.002 p.p.m. for propane by putting pure propane through a silicone grease column. Detection limits of 0.01 p.p.m. on a dimethylsulfolane column and 0.03 p.p.m. on a diisodecylphthalate column were calculated by Feinland, Andreatch, and Cotrupe ( 5 ) ; these limits were based on the actual signals obtained a t higher concentrations of n-butane. I n the present investigation, a detection limit as low as 0.001 p.p.m. was obtained from analyses of complex synthetic and atmospheric mixtures present in concentrations below 0.01 p.p.m. I n comparison with previous methods involving concentration steps, the present one provides a rapid, convenient method for the analysis of light hydrocarbons found in polluted atmospheres. The method also may be used to determine other components by the appropriate selection of other columns or of multiple column arrangements ( 5 ) . LITERATURE CITED
(1) Boggers, J. D., Adams, S . C., ASAL. CHEM.30, 1471 (1958).
(2) Condon, R. D., Scholly, C. J., Averill, W., “Gas Chromatography,” R. P. IT-.
Scott, ed., p. 30, Butterworths, London, 1960. (3) Eggerston, F. T., Nelsen, F. M., ANAL. CHEM.30, 1040 (1958). (4) Farrington. P. S.. Pecsok. R. L.. . ,Meeker,R.’ L., Olson, T. ’J., Ibid.; 31, 1513 (1959). (5) Feinland, R. O., Andreatch, A. J., Cotrupe, D. P., Zbid., 33, 991 (1961). (6) Ong$i,ehong, L., “Gas ChromatoEraphy, R. P. W. Scott, ed., p. i , Butterworths, London, 1960. ( 7 ) Rose. A. H.. Brandt. C. S.. J . A i r ‘ k’ollute’on Cont;ol 24ss0c.’ 10, 331 (1960). (8) West, P. W., Sen, B., Gibson, N. A . , ANAL.CHEM.30, 1390 (1958). RECEIVEDfor review October 10, 1961. Accepted April 2 , 1962. Division of Water and Waste Chemistry, 140th ?*leeting, ACS, Chicago, Ill., September 1961. VOL.
34, NO. 7 , JUNE 1962
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